ASSOC-EQUAL

(Assoc-equal x alist) is the first member of alist whose car
is x, or nil if no such member exists.

(Assoc-equal x alist) has a guard of (alistp alist), and
returns the first member of alist whose car is x, or nil if
no such member exists. Thus, assoc-equal has the same
functionality as the Common Lisp function assoc, except that it
uses the equal function to test whether x is the same as each
successive `key' of alist. See assoc and see assoc-eq.